Ultra-High Strength Stainless Alloy Strip, a Method of Making Same, and a Method of Using Same for Making a Golf Club Head

ABSTRACT

A stainless steel strip article is disclosed. The article is formed from a corrosion resistant alloy having the following composition in weight percent, about: 
     
       
         
               
               
               
             
                   
                   
               
                   
                 C 
                  0.03 max. 
               
                   
                 Mn 
                  1.0 max. 
               
                   
                 Si 
                  0.75 max. 
               
                   
                 P 
                 0.040 max. 
               
                   
                 S 
                 0.020 max. 
               
                   
                 Cr 
                 10.9-11.1 
               
                   
                 Ni 
                 10.9-11.1 
               
                   
                 Mo 
                 0.9-1.1 
               
                   
                 Ti 
                 1.5-1.6 
               
                   
                 Al 
                  0.25 max. 
               
                   
                 Nb 
                 0.7-0.8 
               
                   
                 Cu 
                    1 max. 
               
                   
                 B 
                 0.010 max. 
               
                   
                 N 
                 0.030 max. 
               
                   
                   
               
           
              
             
             
              
              
              
              
              
              
              
              
              
              
              
              
              
              
              
             
          
         
       
     
     The balance is iron and usual impurities. The elongated thin strip article provides a room temperature tensile strength of at least about 280 ksi in the solution treated and age hardened condition. A method of making the strip article and a method of using it to make a golf club are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication No. 61/110,034 filed Oct. 31, 2008, the entirety of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to stainless steel strip material and inparticular to a stainless steel strip article having very high tensilestrength, a method of making same, and a method of using the stripmaterial for making a golf club head.

2. Description of the Related Art

Golf club manufacturers are constantly looking for a high strengthfaceplate material. Very high strength allows the faceplate section tobe made thinner, and therefore lighter, which provides designers moreleeway in club head design. In addition, corrosion-resistant materialsare preferable to non-stainless materials because surface coatings orplating, which could be removed during use, are not required.

Current solutions to this problem include the use of standard PHstainless steel alloys such as the CUSTOM 455 alloy and newly designedstainless alloys such as the CUSTOM 465 and CUSTOM 475 alloys. However,the CUSTOM 455 and CUSTOM 465 alloys do not provide the strength levelsdesired in new club designs. The CUSTOM 475 alloy provides very highstrength, but it is also highly alloyed, making it both expensive forthe club manufacturer as well as less forgiving in the golf clubmanufacturing process.

In addition, many club heads are typically manufactured using a castbody with a faceplate. The cast body material is typically formed of aprecipitation hardenable stainless steel such as 17-4 PH or 15-5 PHstainless steel. Golf clubs are typically manufactured by welding thefaceplate to the cast body and then heat treating the entire assembly todevelop final properties. The alloys typically used for the cast body ofthe club have solution temperatures of about 1900° F., whereas the knownfaceplate materials have solution temperatures ranging from 1550° F. to1000° F. This mismatch in heat treating temperatures results in eitherthe club body, or the faceplate material, or possibly both, providingless than optimum properties in the as-heat treated condition afterassembly of the club head. In addition, the CUSTOM 475 alloy oftenrequires a different manufacturing process altogether, because the alloycannot be re-solutioned after club head assembly.

BRIEF SUMMARY OF THE INVENTION

The disadvantages of the known materials are overcome to a large degreeby a stainless steel strip article according to this invention. Inaccordance with the one aspect of the present invention, there isprovided a stainless steel strip article that is formed from a corrosionresistant alloy comprising, in weight percent, about:

C  0.03 max. Mn  1.0 max. Si  0.75 max. P 0.040 max. S 0.020 max. Cr10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al  0.25 max. Nb 0.7-0.8 Cu   1 max. B 0.010 max. N 0.030 max.and the balance is iron and usual impurities. The elongated thin striparticle provides a room temperature tensile strength of at least about280 ksi in the solution treated and age hardened condition.

In accordance with another aspect of this invention there is provided amethod of making a thin strip article. The method comprises the steps ofcasting a corrosion resistant alloy having the weight percentcomposition set forth above to form an ingot. The ingot is hot worked toform an elongated strip material. The strip material is then heattreated under conditions of time and temperature to provide an ultimatetensile strength of at least about 280 ksi at room temperature.

In accordance with a further aspect of this invention there is provideda method of making a golf club head. The method includes the step ofcasting a corrosion resistant alloy having the weight percentcomposition set forth above to form an ingot. The ingot is hot worked toform an elongated strip article which is then heat treated underconditions of time and temperature to benefit the machinability andprocessability of the strip material. The strip material is thenmachined to form a faceplate for a golf club head. The method includesthe further step of forming a golf club head body from a corrosionresistant precipitation hardenable steel alloy. The faceplate is bondedto golf club head body. The assembly is then heat treated underconditions of time and temperature sufficient to provide a desired levelof hardness and strength in the golf club head body and an ultimatetensile strength of at least about 280 ksi at room temperature in thefaceplate.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph of tensile strength as a function of agingtemperature.

DETAILED DESCRIPTION

A preferred embodiment of the invention includes an elongated striparticle having the following composition in weight percent:

C  0.03 max. Mn  1.0 max. Si  0.75 max. P 0.040 max. S 0.020 max. Cr10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al  0.25 max. Nb 0.7-0.8 Cu   1 max. B 0.010 max. N 0.030 max.The balance is iron and the usual impurities.

The alloy composition is preferably melted using vacuum inductionmelting (VIM). The steel is cast into one or more ingot molds. Foradditional cleanness, the alloy is vacuum arc remelted (VAR) after theVIM step. After solidification, the alloy is formed into strip byintermediate pressing of the ingot to form a billet and then hot rollingthe billet to form elongated strip. Alternatively, the strip materialcan be formed by hot rolling the ingot from a starting temperature ofabout 1000° F. to 2250° F. The strip can be provided in the averagedcondition by heating at about 1100° F. to 1350° F. for about 2 to 8hours and then cooling in air. Alternatively, and for bettermachinability and processability, the strip material is heated at about1900° F. to 1950° F. for about 1 hour, cooled in air, refrigerated atabout −100° F. for about 8 hours, and then warmed in air to roomtemperature. Preferably, the strip material is cold rolled to final ornear final thickness prior to being heat treated. The strip materialaccording to this invention can be solution treated in a continuousfurnace with times and temperatures adjusted accordingly. For the golfclub application, the strip material is processed to a thickness ofabout 0.02-0.16 inches, preferably about 0.10-0.12 inches.

Unlike the known high strength stainless steel alloys such as the CUSTOM475 stainless alloy, the alloy strip according to this invention can bedouble solution treated with no significant loss in properties,particularly no loss of strength. In other words, the stainless steelstrip material of this invention can be provided in the solution treatedplus refrigerated condition, processed into components, and thenre-solutioned, re-refrigerated, and age hardened after being assembledinto a golf club head to provide the desired high strength and hardness.

As an example of the elongated strip article according to the presentinvention, a small heat was melted and processed. The 400 lb heat wasmelted by VIM+VAR and cast as an 8-inch diameter ingot. The weightpercent composition of the VAR ingot is given below in Table I. Thebalance of the alloy was iron and usual impurities.

TABLE I C Mn Si P S Cr Ni Mo Ti Cb B N Ce 0.005 0.05 0.04 <0.005 <0.000511.05 11.02 1.01 1.56 0.79 0.0019 0.0016 0.001The ingot was homogenized at 2300° F. for 16 hours, and then pressed toa 4-in×8-in billet from a starting temperature of 2000° F. The billetwas hot rolled to 7.5 in. wide×0.15 in. thick strip from a startingtemperature of 2250° F. The strip was then ground to 0.135 in. thick andthen cold rolled to 0.1103 in. thick. The strip was given an averagingtreatment by heating at 1146° F. for 5.5 hours. After cooling to roomtemperature, the strip material was ground to a final thickness of0.1083 in.

Standard strip tensile blanks were rough cut in the longitudinal andtransverse orientations from the overaged strip. Groups of the blankswere solution treated at 1850° F., 1900° F., 1950° F., and 2000° F.,respectively, for 1 hour and air cooled. The solution treated blankswere deep chilled at −100° F. for 8 hours and then warmed in air to roomtemperature. The blanks were then rough machined to provide a gagesection about ½ wide×2 inches long. Groups of the rough machined blanksfrom each solution treatment were aged at temperatures ranging fromabout 900° F. to about 975° F. for 4 hours and then air cooled. The testspecimens were finish machined after aging and tested at roomtemperature.

The results of room temperature tensile and hardness testing arepresented in Tables 2-4 below including the solution treatmenttemperature (Solution Temp.) and the aging temperature (Age Temp.) in °F., the 0.2% offset yield strength (Y.S.) and ultimate tensile strength(U.T.S.) in ksi, and the Rockwell C-scale hardness (Hardness) as HRC.

TABLE 2 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi)(ksi) % El. (HRC) 1850° F. 950° F. L 258 266 — 52.0 258 267 — 258 268 —T 260 272 — 260 273 — 245 272 — 975° F. L 244 252 — 50.5 244 253 — 245253 — T 248 258 — 246 256 — 245 255 —

TABLE 3 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi)(ksi) % El. (HRC) 1900° F. 900° F. L 260 284 4.8 53.5 261 286 4.3 259284 4.8 T 264 287 4.3 257 282 2.8 258 285 4.2 925° F. L 259 282 4.0 53.5257 281 4.2 256 281 4.1 T 247 285 3.9 260 285 4.1 257 285 4.2 950° F. L250 274 6.2 52.0 252 273 6.7 249 273 6.4 T 251 277 6.5 250 277 6.0 251276 6.7 975° F. L 234 258 7.3 50.5 235 256 7.1 235 259 6.9 T 243 264 6.8240 261 6.6 242 263 6.6

TABLE 4 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi)(ksi) % El. (HRC) 1950° F. 900° F. L * * 4.6 53.5 * * 4.1 * * 4.7 T * *5.4 * * 4.2 * * 4.8 950° F. L * * 5.3 52.5 * * 5.2 * * 4.3 T 264 275 5.3267 279 4.9 260 276 5.3 2000° F. 900° F. L 248 282 5.9 53.5 253 283 5.0255 282 5.5 T 261 286 4.6 258 291 5.1 260 287 4.7 950° F. L 253 276 5.753.0 254 277 5.2 255 276 5.2 T 260 281 4.7 261 282 4.6 263 282 5.0 *Strength data was lost for these samples. However, the test operatorrecalls that the U.T.S. for the H900 samples was above 280 ksi and thatthe U.T.S. for the H950 samples was slightly under 280 ksi

Metallographic analysis of the test specimens showed that the materialsolution treated at 1850° F. and 1900° F. had a grain size of about ASTM8. The material solution treated at 1950° F. had a grain size of aboutASTM 7-8. The material solution treated at 2000° F. had a grain size ofabout ASTM 2-3. Here and throughout this application, the ASTM grainsize means average grain size as determined in accordance with ASTMStandard Test Procedure E-112.

The results presented in Tables 2, 3, and 4 show that the preferredsolution temperature is about 1900° F. to about 1950° F. Likewise, thepreferred aging temperature is about 900° F. to 925° F. in order for thematerial to provide the desired 280 ksi U.T.S. A graph of U.T.S. versussolution and aging temperature combinations is shown in the drawing.

The data presented in the tables show that a strip article made from thealloy composition described in this application is capable of attainingan U.T.S. 280 ksi or higher. The strip material is much less heavilyalloyed than other stainless compositions capable of that strengthlevel, resulting in a lower alloy cost. In addition, the strip materialis capable of being solution heat treated more than once withoutsacrificing strength or toughness properties. The strip material of thisinvention is preferably solution heat treated at a temperature in rangeof about 1900-1950° F., making golf club faceplates of this compositionfully compatible with the solution treating temperature for theprecipitation hardenable stainless casting alloys most often used forthe body of golf club head. Therefore, the faceplate and the club headbody can be solution treated and age hardened in the assembledconfiguration to develop maximum hardness and strength, not only in thebody of the club head, but also in the faceplate which makes contactwith a golf ball.

It will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. It isunderstood, therefore, that the invention is not limited to theparticular embodiments that are described, but is intended to cover allmodifications and changes within the scope and spirit of the inventionas described above and set forth in the appended claims.

1. An elongated, thin strip article that is formed from corrosionresistant alloy comprising, in weight percent, about: C  0.03 max. Mn 1.0 max. Si  0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al  0.25 max. Nb 0.7-0.8 Cu    1 max. B0.010 max. N 0.030 max.

and the balance is iron and usual impurities, said elongated thin striparticle having a room temperature tensile strength of at least about 280ksi in the solution treated and age hardened condition.
 2. An elongatedstrip article as claimed in claim 1 wherein the strip has a thickness ofabout 0.02 to 0.16 inches.
 3. An elongated strip article as claimed inclaim 1 wherein the alloy has an average grain size not greater thanabout ASTM 7-8 in major dimension.
 4. An elongated strip article asclaimed in claim 1 which has a hardness of about 53-54 HRC.
 5. A methodof making a thin strip article comprising the steps of casting acorrosion resistant alloy comprising, in weight percent, about C  0.03max. Mn  1.0 max. Si  0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al  0.25 max. Nb 0.7-0.8 Cu    1 max.B 0.010 max. N 0.030 max.

and the balance being iron and usual impurities to form an ingot;mechanically working said ingot to form an elongated strip material; andthen heat treating said elongated strip material under conditions oftime and temperature to provide an ultimate tensile strength of at leastabout 280 ksi at room temperature.
 6. A method as claimed in claim 5wherein the step of heat treating the elongated strip material comprisesthe steps of: heating the elongated strip material at a temperature ofabout 1900-2000° F.; and then heating the elongated strip material at atemperature of about 900° F. to about 950° F.
 7. A method as claimed inclaim 6 wherein the first heating step comprises heating the alloy at atemperature of about 1900-1950° F. and the method comprises thefollowing steps between the heating steps: rapidly cooling the alloy toabout −100° F.; and then holding the alloy at about −100° F. for aperiod of time to substantially completely transform any austenite inthe alloy to martensite.
 8. A method as claimed in claim 5 wherein thestep of mechanically working the ingot comprises the steps of: pressingthe ingot to form a billet; and then hot rolling the billet to form theelongated strip material.
 9. A method as claimed in claim 5 wherein thestep of mechanically working the ingot comprises hot rolling the ingotto form the elongated strip material.
 10. A method as claimed in claim 9wherein the hot rolling step comprises heating the billet to about1900-2250° F.
 11. A method of making a golf club head comprising thesteps of casting a corrosion resistant alloy comprising, in weightpercent, about C  0.03 max. Mn  1.0 max. Si  0.75 max. P 0.040 max. S0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al  0.25 max.Nb 0.7-0.8 Cu    1 max. B 0.010 max. N 0.030 max.

and the balance being iron and usual impurities to form an ingot;mechanically working said ingot to form an elongated strip material;heat treating said elongated strip material under conditions of time andtemperature to improve the machinability and processability of thematerial; cutting said elongated strip material to form a faceplate fora golf club head; forming a golf club head body from a corrosionresistant precipitation hardenable steel alloy; bonding said faceplateto said golf club head body to form a golf club head assembly; and thenheat treating said golf club head assembly under conditions of time andtemperature to provide hardness and strength in the golf club headassembly and an ultimate tensile strength of at least about 280 ksi atroom temperature in said faceplate.
 12. A method as claimed in claim 11wherein the step of heat treating the golf club heat assembly comprisesthe steps of: heating the elongated strip material at a temperature ofabout 1900-2000° F.; and then heating the elongated strip material at atemperature of about 900° F. to about 950° F.
 13. A method as claimed inclaim 12 wherein the first heating step comprises heating the golf clubheat assembly at a temperature of about 1900-1950° F. and the methodcomprises the following steps between the heating steps: rapidly coolingthe golf club head assembly to about −100° F.; and then holding the golfclub head assembly at about −100° F. for a period of time tosubstantially completely transform any austenite in the alloy tomartensite.
 14. A method as claimed in claim 11 wherein the step ofmechanically working the ingot comprises the steps of: pressing theingot to form a billet; and then hot rolling the billet to form theelongated strip material.
 15. A method as claimed in claim 11 whereinthe step of mechanically working the ingot comprises hot rolling theingot to form the elongated strip material.
 16. A method as claimed inclaim 15 wherein the hot rolling step comprises heating the billet toabout 1900-2250° F.
 17. A method as claimed in claim 11 wherein the stepof heat treating the elongated strip material comprises the step ofoveraging the strip material at about 1100-1350° F.
 18. A method asclaimed in claim 11 wherein the step of mechanically working the ingotcomprises the steps of: pressing the ingot to form a billet; hot rollingthe billet to form the elongated strip material; and then cold rollingthe elongated strip material to reduce its thickness to final or nearfinal dimension.
 19. A method as claimed in claim 11 wherein the step ofmechanically working the ingot comprises the steps of: hot rolling theingot to form elongated strip material; and then cold rolling theelongated strip material to reduce its thickness to final or near finaldimension.
 20. A method as claimed in claim 18 wherein the hot rollingstep comprises heating the ingot or billet to about 1038-1232° C.
 21. Amethod as claimed in claim 19 wherein the hot rolling step comprisesheating the ingot or billet to about 1038-1232° C.